Efeito da velocidade de aquecimento nas propriedades de produtos da cerâmica estrutural

Heating rate is one of the main variables that determine a fire cycle. In industrial processes that use high temperatures, greater fire great can reduce the cost of production and increase productivity. The use of faster and more efficient fire cycles has been little investigated by the structural ceramic industry in Brazil. However, one of the possibilities that aims at modernizing the sector is the use of roller kilns and the inclusion of natural gas as fuel. Thus, the purpose of this study is to investigate the effect of heating rate on the technological properties of structural ceramic products. Clay raw materials from the main ceramic industries in the state of Rio Grande do Norte were characterized. Some of the raw materials characterized were formulated to obtain the best physical and mechanical properties. Next, raw materials and formulations were selected to study the influence of heating rate on the final properties of the ceramic materials. The samples were shaped by pressing and extrusion and submitted to rates of 1 °C/min, 10 °C/min and 20 °C/min, with final temperatures of 850 °C, 950 °C and 1050 °C. Discontinuous cycles with rates of 10 °C/min or 15 °C/min up to 600 °C and a rate of 20 °C/min up to final temperature were also investigated. Technological properties were determined for all the samples and microstructural analysis was carried out under a number of fire conditions. Results indicate that faster and more efficient fire cycles than those currently in practice could be used, limiting only some clay doughs to certain fire conditions. The best results were obtained for the samples submitted to slow cycles up to 600 °C and fast fire sinterization up to 950 °C. This paper presents for the first time the use of a fast fire rate for raw materials and clay formulations and seeks to determine ideal dough and processing conditions for using shorter fire times, thus enabling the use of roller kilns and natural gas in structural ceramic industries

Controle vetorial de velocidade de uma máquina de indução sem mancais trifásica com bobinado dividido utilizando estimação neural de fluxo

This work describes the study and the implementation of the vector speed control for a three-phase Bearingless induction machine with divided winding of 4 poles and 1,1 kW using the neural rotor flux estimation. The vector speed control operates together with the radial positioning controllers and with the winding currents controllers of the stator phases. For the radial positioning, the forces controlled by the internal machine magnetic fields are used. For the radial forces optimization , a special rotor winding with independent circuits which allows a low rotational torque influence was used. The neural flux estimation applied to the vector speed controls has the objective of compensating the parameter dependences of the conventional estimators in relation to the parameter machine s variations due to the temperature increases or due to the rotor magnetic saturation. The implemented control system allows a direct comparison between the respective responses of the speed and radial positioning controllers to the machine oriented by the neural rotor flux estimator in relation to the conventional flux estimator. All the system control is executed by a program developed in the ANSI C language. The DSP resources used by the system are: the Analog/Digital channels converters, the PWM outputs and the parallel and RS-232 serial interfaces, which are responsible, respectively, by the DSP programming and the data capture through the supervisory system

Controle vetorial de velocidade de um motor de indução trifásico com estimação neural de fluxo

This work describes the study and the implementation of the speed control for a three-phase induction motor of 1,1 kW and 4 poles using the neural rotor flux estimation. The vector speed control operates together with the winding currents controller of the stator phasis. The neural flux estimation applied to the vector speed controls has the objective of compensating the parameter dependences of the conventional estimators in relation to the parameter machine s variations due to the temperature increases or due to the rotor magnetic saturation. The implemented control system allows a direct comparison between the respective responses of the speed controls to the machine oriented by the neural rotor flux estimator in relation to the conventional flux estimator. All the system control is executed by a program developed in the ANSI C language. The main DSP recources used by the system are, respectively, the Analog/Digital channels converters, the PWM outputs and the parallel and RS-232 serial interfaces, which are responsible, respectively, by the DSP programming and the data capture through the supervisory system

Controle vetorial para velocidade de um motor de indução trifásico utilizando estimador filtro de Kalman

This paper describes the study, computer simulation and feasibility of implementation of vector control speed of an induction motor using for this purpose the Extended Kalman Filter as an estimator of rotor flux. The motivation for such work is the use of a control system that requires no sensors on the machine shaft, thus providing a considerable cost reduction of drives and their maintenance, increased reliability, robustness and noise immunity as compared to control systems with conventional sensors

Função de distribuição generalizada aplicada à velocidade de rotação estelar

In the present work we use a Tsallis maximum entropy distribution law to fit the observations of projected rotational velocity measurements of stars in the Pleiades open cluster. This new distribution funtion which generalizes the Ma.xwel1-Boltzmann one is derived from the non-extensivity of the Boltzmann-Gibbs entropy. We also present a oomparison between results from the generalized distribution and the Ma.xwellia.n law, and show that the generalized distribution fits more closely the observational data. In addition, we present a oomparison between the q values of the generalized distribution determined for the V sin i distribution of the main sequence stars (Pleiades) and ones found for the observed distribution of evolved stars (subgiants). We then observe a correlation between the q values and the star evolution stage for a certain range of stel1ar mass

Criação da matéria em cosmologias com velocidade da luz variável e eletrônico não-linear

In this work we obtain the cosmological solutions and investigate the thermodynamics of matter creation in two diferent contexts. In the first we propose a cosmological model with a time varying speed of light c. We consider two diferent time dependence of c for a at Friedmann-Robertson- Walker (FRW) universe. We write the energy conservation law arising from Einstein equations and study how particles are created as c decreases with cosmic epoch. The variation of c is coupled to a cosmological Λ term and both singular and non-singular solutions are possible. We calculate the "adiabatic" particle creation rate and the total number of particles as a function of time and find the constrains imposed by the second law of thermodynamics upon the models. In the second scenario, we study the nonlinearity of the electrodynamics as a source of matter creation in the cosmological models with at FRW geometry. We write the energy conservation law arising from Einstein field equations with cosmological term Λ, solve the field equations and study how particles are created as the magnetic field B changes with cosmic epoch. We obtain solutions for the adiabatic particle creation rate, the total number of particles and the scale factor as a function of time in three cases: Λ = 0, Λ = constant and Λ α H2 (cosmological term proportional to the Hubble parameter). In all cases, the second law of thermodynamics demands that the universe is not contracting (H ≥ 0). The first two solutions are non-singular and exhibit in ationary periods. The third case studied allows an always in ationary universe for a suficiently large cosmological term

Modelos cosmológicos com velocidade da luz variável

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Velocidade da marcha como preditor de fragilidade em uma amostra populacional de idosos brasileiros

Gait speed has been described as a predictive indicator of important adverse outcomes in older populations. Among the criteria to evaluate frailty, gait speed has been identified as the most reliable predictor of fragility, practical and low cost. Objective: This study assesses the discriminating capability of gait speed in determining the presence of fragility in the elderly community in northeast of Brazil. Method: We performed an observational analytic study with a transversal character with a sample of 391 community-living elders, aged 65 years or older, of both sexes, in the city of Santa Cruz-RN. Participants were interviewed using a multidimensional questionnaire to obtain sociodemographic information, physical-related and mental health-related information. The unintentional weight loss, muscle weakness, self-reported exhaustion, slow gait and low-physical activity were considered to evaluate the frailty syndrome. Gait velocity was measured as the time taken to walk the middle 4,6 meters of 8,6 meters (excluding 2 meters to warm-up phase and 2 meters to deceleration phase).We calculate the sensitivity and specificity of gait speed test in different cutoff points for the test run time, from which ROC curve was constructed as a measure of test predictive value to identify frail elders. The prevalence of frailty in Santa Cruz-RN was 17.1%. The gait speed test accuracy was 71%when speed is below 0,91m/s. Among women, the gait speed test accuracy was 80%(gait speed below 0.77m/s) and among men, the test accuracy was 86% (gait spend below 0,82%) (p<0,0001).Conclusion: our findings have clinical relevance when we consider that the detection of frailty presence by the gait speed test can be observed in elderly men and women by a simple, cheap and efficient exam

Regulador eletromagnético de frequência aplicado no controle de velocidade de geradores eólicos

The constant necessity for new sources of renewable energy is increasingly promoting the increase of investments in this area. Among other sources, the wind power has been becoming prominent. It is important to promote the search for the improvement of the technologies involved in the topologies of the wind turbines, seeking for alternatives which enhance the gotten performance, despite the irregularity of the wind speed. This study presents a new system for speed control, in this case applied to the wind turbines - the Electromagnetic Frequency Regulator (EFR). One of the most used devices in some topologies is the mechanical gearboxes which, along with a short service life, often represent sources of noise and defects. The EFR does not need these transmission boxes, representing a technological advancement, using for that an adapted induction machine, in which the stator becomes mobile, supportive to the axis of the turbine. In the topology used in this study, the EFR also allows us to leave out the usage of the eletronic converters to establish the coupling between the generator and the electrical grid. It also the reason why it provides the possibility of obtaining the generation in alternating current, with constant voltage and frequency, where there is no electrical grid. Responsable for the mechanical speed control of the generator, the EFR can be useful in other transmission systems in which the mechanical speed control output is the objective. In addition, the EFR operates through the combination of two inputs, a mechanical and other electrical. It multiplies the possibilities of application because it is able to synergistic coupling between different arrays of energy, and, for such reasons, it enables the various sources of energy involved to be uncoupled from the network, being the synchronous generator responsible for the system connection with the electrical grid, simplifying the control strategies on the power injected in it. Experimental and simulation results are presented through this study, about a wind turbine, validating the proposal related to the efficience in the speed control of the system for different wind conditions.

Proposta de válvula bypass para controle de velocidade de PIGs instrumentados: protótipo e simulação em bancada

In the Oil industry, oil and gas pipelines are commonly utilized to perform the transportation of production fluids to longer distances. The maintenance of the pipelines passes through the analysis of several tools, in which the most currently used are the pipelines inspection cells, popularly knowing as PIG. Among the variants existing in the market, the instrumented PIG has a significant relevance; acknowledging that through the numerous sensors existing in the equipment, it can detect faults or potential failure along the inspected line. Despite its versatility, the instrumented PIG suffers from speed variations, impairing the reading of sensors embedded in it. Considering that PIG moves depending on the speed of the production fluid, a way to control his speed is to control the flow of the fluid through the pressure control, reducing the flow rate of the produced flow, resulting in reduction of overall production the fluid in the ducts own or with the use of a restrictive element (valve) installed on it. The characteristic of the flow rate/pressure drop from restrictive elements of the orifice plate is deducted usually from the ideal energy equation (Bernoulli’s equation) and later, the losses are corrected normally through experimental tests. Thus, with the objective of controlling the fluids flow passing through the PIG, a valve shutter actuated by solenoid has been developed. This configuration allows an ease control and stabilization of the flow adjustment, with a consequent response in the pressure drops between upstream and downstream of the restriction. It was assembled a test bench for better definition of flow coefficients; composed by a duct with intern diameter of four inches, one set of shutters arranged in a plate and pressure gauges for checking the pressure drop in the test. The line was pressurized and based on the pressure drop it was possible to draw a curve able to characterize the flow coefficient of the control valve prototype and simulate in mockup the functioning, resulting in PIG speed reduction of approximately 68%.

Efeito da velocidade de aquecimento nas propriedades de produtos da cerâmica estrutural

Heating rate is one of the main variables that determine a fire cycle. In industrial processes that use high temperatures, greater fire great can reduce the cost of production and increase productivity. The use of faster and more efficient fire cycles has been little investigated by the structural ceramic industry in Brazil. However, one of the possibilities that aims at modernizing the sector is the use of roller kilns and the inclusion of natural gas as fuel. Thus, the purpose of this study is to investigate the effect of heating rate on the technological properties of structural ceramic products. Clay raw materials from the main ceramic industries in the state of Rio Grande do Norte were characterized. Some of the raw materials characterized were formulated to obtain the best physical and mechanical properties. Next, raw materials and formulations were selected to study the influence of heating rate on the final properties of the ceramic materials. The samples were shaped by pressing and extrusion and submitted to rates of 1 °C/min, 10 °C/min and 20 °C/min, with final temperatures of 850 °C, 950 °C and 1050 °C. Discontinuous cycles with rates of 10 °C/min or 15 °C/min up to 600 °C and a rate of 20 °C/min up to final temperature were also investigated. Technological properties were determined for all the samples and microstructural analysis was carried out under a number of fire conditions. Results indicate that faster and more efficient fire cycles than those currently in practice could be used, limiting only some clay doughs to certain fire conditions. The best results were obtained for the samples submitted to slow cycles up to 600 °C and fast fire sinterization up to 950 °C. This paper presents for the first time the use of a fast fire rate for raw materials and clay formulations and seeks to determine ideal dough and processing conditions for using shorter fire times, thus enabling the use of roller kilns and natural gas in structural ceramic industries

O paradigma tecnológico e a revolução informacional: fundamentos da sociedade da informação

REGIS, Josiana Florencio Vieira; CAMPOS, Ana Celia Cavalcanti Fernandes. O paradigma tecnologico e a revoluçao informacional: fundamentos da sociedade da informaçao. In: CONGRESSO INTERNACIONAL EM SISTEMAS DE INFORMAÇAO E GESTAO DA TECNOLOGIA, 6., 2009. Sao Paulo. Anais eletronicos... Sao Paulo: FEA/USP, 2009. Trabalho oral.

Efeitos da simpaticotomia endoscópica sobre as artérias carótidas e vertebrais na terapêutica cirúrgica da hiperidrose primária

Analisar, em pacientes submetidos a simpaticotomia videotoracoscópica para tratamento da Hiperidrose Primária (HP), as conseqüências hemodinâmicas da desnervação vascular das artérias carótidas e vertebrais após a trans-secção cirúrgica da cadeia simpática torácica (simpaticotomia), através da mensuração de parâmetros ultra-sonográficos. Método: Vinte e quatro pacientes portadores de HP submetidos a quarenta e oito simpaticotomias torácicas endoscópicas foram avaliados através da mensuração da velocidade de pico sistólico (VPS), velocidade de pico diastólico (VPD), índice de pulsatibilidade (IP) e índice de resistência (IR) nas artérias carótidas comuns, internas e externas, além da artéria vertebral bilateralmente usando o eco-doppler duplex scan. As avaliações foram realizadas antes da intervenção cirúrgica e trinta dias após o procedimento. O teste de Wilcoxon foi usado na análise das diferenças entre as variáveis antes e depois da simpaticotomia. Resultados: A simpaticotomia no nível de T3 foi a trans-secção mais realizada (95,83%), seja isoladamente (25%) ou associada a T4 (62,50%) ou a T2 (8,33%). Houve aumento significativo no IR e no IP da artéria carótida comum bilateralmente (p<0,05). A VPD da artéria carótida interna diminuiu em ambos os lados (p<0,05). A VPS e a VPD da artéria vertebral direita também aumentaram (p<0,05). Achados assimétricos foram observados, de modo que artérias do lado direito foram as mais freqüentemente afetadas. Conclusões: Alterações hemodinâmicas foram observadas nas artérias vertebral e carótida após simpaticotomia para tratamento de HP. VPS foi o parâmetro mais freqüentemente alterado, principalmente nas artérias do lado direito, representando alterações assimétricas significantes nas artérias carótida e vertebral. Entretanto, são necessárias pesquisas subseqüentes para verificar se essas alterações são definitivas ou temporárias, uma vez que as inferências clínicas somente terão validação se as alterações forem permanentes

O ambiente de pesquisas virtuais na biblioteca acadêmica: da implantação à consolidação, um longo percurso.

O ambiente da pesquisa acadêmica nas bibliotecas universitárias se apresenta em constante evolução. Nesta perspectiva, as construções de novos espaços se fazem necessários na promoção e acesso à informação, via vários tipos de suportes. Atualmente, antigos paradigmas são sobrepostos com uma velocidade luz. Neste artigo, apresenta-se a implantação, manutenção e consolidação do Setor de Pesquisas Virtuais em uma biblioteca universitária, com vistas à democratização do acesso à informação eletrônica, como também à criação de uma rede de comunicação rápida, eficaz, tendo como foco central as novas Tecnologias da Informação e Comunicação (TICs). Assim, enfoca-se a construção do espaço físico do Setor de Pesquisas Virtuais, através da criação de normas, produtos, serviços e divulgação desse novo recurso. A consolidação deste espaço encontra-se em pleno desenvolvimento, via aquisição de produtos específicos, consorciamentos junto às redes especializadas, geração de novos produtos e, principalmente, a presença direta de um profissional bibliotecário intervindo e mediando o processo da busca e do acesso às informações com segurança e confiabilidade das fontes. Consequentemente, essas ações estão trazendo benefícios à comunidade atendida.

Teoria de carteiras e a alocação de parques eólicos offshore

The consumption of energy on the planet is currently based on fossil fuels. They are responsible for adverse effects on the environment. Renewables propose solutions for this scenario, but must face issues related to the capacity of the power supply. Wind energy offshore emerging as a promising alternative. The speed and stability are greater winds over oceans, but the variability of these may cause inconvenience to the generation of electric power fluctuations. To reduce this, a combination of wind farms geographically distributed was proposed. The greater the distance between them, the lower the correlation between the wind velocity, increasing the likelihood that together achieve more stable power system with less fluctuations in power generation. The efficient use of production capacity of the wind park however, depends on their distribution in marine environments. The objective of this research was to analyze the optimal allocation of wind farms offshore on the east coast of the U.S. by Modern Portfolio Theory. The Modern Portfolio Theory was used so that the process of building portfolios of wind energy offshore contemplate the particularity of intermittency of wind, through calculations of return and risk of the production of wind farms. The research was conducted with 25.934 observations of energy produced by wind farms 11 hypothetical offshore, from the installation of 01 simulated ocean turbine with a capacity of 5 MW. The data show hourly time resolution and covers the period between January 1, 1998 until December 31, 2002. Through the Matlab R software, six were calculated minimum variance portfolios, each for a period of time distinct. Given the inequality of the variability of wind over time, set up four strategies rebalancing to evaluate the performance of the related portfolios, which enabled us to identify the most beneficial to the stability of the wind energy production offshore. The results showed that the production of wind energy for 1998, 1999, 2000 and 2001 should be considered by the portfolio weights calculated for the same periods, respectively. Energy data for 2002 should use the weights derived from the portfolio calculated in the previous time period. Finally, the production of wind energy in the period 1998-2002 should also be weighted by 1/11. It follows therefore that the portfolios found failed to show reduced levels of variability when compared to the individual production of wind farms hypothetical offshore